The present invention relates to a klystron tuning mechanism and, more particularly, to a klystron tuning mechanism for amplifying a high frequency power in a millimeter frequency region.
A klystron is basically constituted by an electron gun section for generating and emitting an electron beam, a high-frequency circuit section for causing high-frequency power to interact with the electron beam, a collector section for catching the electron beam, and a focusing unit for focusing the electron beam passing through the high-frequency circuit section. The high-frequency circuit section is generally constituted by a plurality of cavity resonators. Each cavity resonator has a resonance cavity main body and a tuning element arranged in a resonance cavity to variably change the tuning frequency. The tuning element is connected/supported to/by a tuning mechanism located outside the cavity resonator such that the element can be displaced in the resonance cavity.
In such a klystron, every time the frequency of high-frequency power to be amplified is changed, the tuning frequency must be adjusted to a proper value while the waveforms of outputs from the plurality of cavity resonators are observed. In order to solve the problem of difficulty in handling as compared with a traveling-wave tube designed to amplify a high frequency in a millimeter frequency region similar to the klystron, a preset mechanism section is arranged to allow the klystron to easily obtain a specified bandwidth by only performing a switching operation with respect to preset frequencies.
A conventional klystron tuning mechanism including such a preset mechanism section comprises a tuning support mechanism, a preset section, and a driving mechanism. The tuning support mechanism has a tuner shaft which is arranged coaxially with a tuning element and connected thereto to support the tuning element at a preset position. In this case, the tuning element is designed to change the tuning frequency by changing the volume of a resonance cavity. The preset section has a plurality of adjustment screws which are adjusted for preset frequencies in advance, and a preset plate which is caused to slide while the adjustment screws are supported thereon, thereby positioning a desired adjustment screw coaxially with the distal end portion of the tuner shaft. The driving mechanism causes the preset section to move forward and backward with respect to the tuning support mechanism so as to bring a selected adjustment screw into contact with the distal end portion of the tuner shaft.
In changing the tuning frequency, the driving mechanism causes the preset section to move backward from the tuning support mechanism so as to free the adjustment screw from the tuner shaft, with which the screw has been in contact, and the preset plate is caused to slide to position an adjustment screw set to a desired frequency to the distal end portion of the tuner shaft. Thereafter, the preset section is moved forward to the tuning support mechanism to be located at a predetermined lock position by the driving mechanism. With this operation, the adjustment screw is brought into contact with the distal end portion of the tuner shaft to push the tuner shaft, and a tuning element coupled to the tuner shaft is positioned to a predetermined position by the tuning support mechanism, thus switching the frequency.
As shown in FIG. 3, in order to prevent looseness of each adjustment screw 13 which is in contact with a distal end portion 7a of a tuner shaft, a groove 13a is formed in the surface of each adjustment screw 13, and a Teflon member 28 is embedded in the groove 13a to be meshed with an internal thread portion 27 formed in preset section 11.
According to a tuning mechanism having this conventional structure, looseness of each adjustment screw 13 is caused by degradation of the Teflon member 28 due to repetitive rotation of the adjustment screw, which is performed for tuning frequency adjustment, and degradation of the Teflon member 28 over time. As a result, the tuning frequency of a cavity resonator deviates from an adjusted value, and the frequency characteristics of the klystron may greatly change within a period of time shorter than the specified service life of the klystron.